This invention relates to a magnetic alloy, particularly, to a corrosion resistant magnetic alloy very suitable for use as a magnetic shielding material.
Permalloy, which is a Ni-Fe type alloy, is well known as a magnetic alloy. In particular, "45 permalloy" containing 45% by weight of Ni is widely used as a magnetic shielding material. This alloy is relatively small in Ni content among various kinds of Permalloy.
This alloy (45 Permalloy), however, tends to rust if exposed to humid circumstances. The rusting is caused even under the ordinary atmosphere in the course of its long period of use. Accordingly, anti-corrosion treatment is required if 45 Permalloy is used as a magnetic shielding material.
Chromium is considered effective for improving the corrosion resistance of Ni-Fe type alloy. However, the Cr addition was considered unfavorable in terms of the magnetic property, of the resultant alloy. Under the circumstances, it is attempted recently to add Si or the like to Ni-Fe-Cr type alloy in order to produce an alloy satisfactory in both corrosion resistance and magnetic property. Alloys of this type are reported in Japanese Patent Application Publication No. 2491/76 and Japanese Patent Application Disclosure No. 114,517/74.
However, the Ni-Fe-Cr alloy of these types is said to necessitate at least 35% by weight of Ni. If the Ni content is less than 35%, the alloy is said to be quite unsatisfactory in magnetic property, rendering the alloy unsuitable for actual uses. The alloy containing such a large amount of expensive Ni is uneconomical. Naturally, it is of high concern in the field to produce an alloy having a smaller Ni content.